1. Field of the Invention
The present invention relates to an image forming apparatus and method, and more particularly, to an image forming apparatus and method capable of obtaining an optimum amount of developer for a uniform density of the developer in a developing area and determining the optimum amount as a default value in order to provide optimum image quality.
2. Description of the Related Art
Generally, electrophotographic image forming apparatuses develop an electrostatic latent image formed on a photoconductive body into a visible image using a developer and transfer the visible image onto a printing medium, thereby printing a desired image. For the developer, a one-property developer that is non-magnetic and a two-property developer which is magnetic are generally used.
The two-property developer is a mixture of toner and carrier in a predetermined ratio. The carrier is attached on a surface of a developing sleeve by a magnetic force of the developing sleeve, and the toner is attached by surrounding static electricity.
FIG. 1 is a sectional view schematically showing the structure of a developing device of an image forming apparatus using the two-property developer.
Referring to FIG. 1, a developing device 10 comprises a housing 11, a developing roller 13, a developer mixing roller 17, a developer agitating screw 18 and a magnetic bar 19.
The housing 11 includes therein the developing roller 13 and the developer agitating screw 18, and has an opening 11a opposite to a photoconductive medium 20 so that the developing roller 13 and the photoconductive medium 20 face each other.
The developing roller 13 comprises a developing sleeve 14 and a fixing magnet 15. The developing sleeve 14 has a tubular form and is rotatably mounted in the housing 11. The developing sleeve 14 transfers a developer 1 to a developing area A, which is opposite to the photoconductive medium 20. The fixing magnet 15 is mounted within the developing sleeve 14 and has a tubular form divided into a plurality of sections. The fixing magnet 15 has a magnetic pole N1 opposite to the developing area A, and magnetic poles S1, N2, N3 and N2 are sequentially formed from the magnetic pole N1 counterclockwise, as shown in FIG. 1. In addition, a developer blade 16 is formed at a certain distance from one portion of the developing sleeve 14 in order to restrict thickness of the developer attached to the developing sleeve 14 to a certain degree.
The developer mixing roller 17 is disposed behind the developing sleeve 14 to evenly agitate two components of the developer 1, which are the toner and carrier, thereby frictionally electrifying the developer 1.
The developer agitating screw 18 is disposed behind the mixing roller 17 to supply the developer 1 to the developer mixing roller 17.
The magnetic bar 19 is disposed at upper and lower outsides of the opening 11a to adsorb the developer scattered in the developing area A.
Hereinbelow, the operation of the developing device 10 having the above structure will be described.
The developer 1 supplied to the housing 11 is supplied to the developer mixing roller 17 by the developer agitating screw 18, so that the toner and carrier are evenly mixed. The agitated developer 1 is attached to the developing sleeve 14 by a magnetic force of the fixing magnet 15 mounted inside the developing sleeve 14, thereby configuring a magnetic brush. As the developing sleeve 14 rotates, the developer 1 attached to the developing sleeve 14 is thinned to a certain thickness, passing through the developer blade 16.
When the developing sleeve 14 is located in the developing area A while rotating, the developer 1 thinned on a surface of the developing sleeve 14 is moved to the photoconductive medium 20 by static electricity of an electrostatic latent image of the photoconductive medium 20, thereby forming an electrostatic latent image. At this time, the developer 1 which is not electrified enough may be scattered without developing the electrostatic latent image. The scattered developer 1 is prevented by the magnetic bar 19 from being discharged out of the developing device 19.
However, such ability of the magnetic bar 19 that prevents scatter of the developer 1 is limited. Therefore, electrification of the developer 1 needs to be in a certain range in order to prevent scatter of the developer 1. Especially, since a consumed amount of the developer 1 per a unit time increases for a fast printing, the developer 1 should be promptly supplied, and also well mixed and agitated in a short time, so that the supplied developer 1 is uniformly electrified as a whole. However, if the developer 1 is excessively or insufficiently supplied, electrification of the developer 1 may be poorly performed, thereby deteriorating image quality or causing the scatter of the developer 1. As a result, a proper amount of the developer 1 for supply, for an optimum image quality, needs to be determined as a default value in an image forming apparatus.